Stent delivery systems proposed heretofore are used to secure a lumen or a space in a body cavity by implanting the stent at the lumen, the stenosed portion or the closed portion of the body cavity in an internal organ such as a blood vessel, bile duct, trachea, esophagus, ureter, digestive tract, and the like.
Stents delivered by the stent delivery system are classified as balloon expandable stents and self-expandable stents, depending upon the function of the stent and the implantation method.
The balloon expandable stent itself has no expanding function. To implant the stent at a desired portion, after the stent is inserted into the desired portion, a balloon disposed in the stent is inflated to expand (plastic deformation) the stent by an expansive force of the balloon so that the stent is fixed, with the stent in close contact with the inner surface of the desired portion of the lumen.
It is necessary to perform the above-described operation of expanding the stent of this type in implanting it in the desired portion. The stent can be implanted in the desired portion by directly mounting it on the contracted balloon. Thus the balloon expandable stent does not have a problem in this respect.
On the other hand, the self-expandable stent itself has contracting and expanding functions. To implant the stent at a desired portion, after it is inserted into the desired portion in a contracted state, a stress applied for maintaining the contracted state is released. For example, the stent is accommodated in a sheath having a smaller diameter than the inner diameter of the desired portion of the lumen by contracting the stent. After the distal end of the sheath reaches the desired portion, the stent is pressed out of the sheath. Because the stent is released from the sheath, the applied stress is removed. The stent thus returns to the original configuration. Thereby the stent adheres to the inner surface of the desired portion.
Because the stent itself has an expandable force, it is unnecessary to perform the operation of expanding the stent of this type while implanting it in the desired portion, unlike the balloon expandable stent. Further there is no possibility that the diameter of the stent becomes smaller due to the pressure of the blood vessel and that a restenosis occurs again.
But compared with the balloon expandable stent, it is difficult to implant the self-expandable stent correctly at the desired portion for the reason described below. In the balloon expandable stent, after the stent is disposed at a desired stenosed portion, a liquid is injected into a balloon. Thus the stent does not move longitudinally when the stent is expanded. The delivery system of the self-expandable stent has a construction in which the stent is restrictedly accommodated between an inner tube and an outer tube, and a locking portion for restricting the movement of the stent is provided on the inner tube at a position located at the proximal side of the stent. By pulling the outer tube toward the proximal side of a system, the stent is released from the restricted state and expands itself. The stent is liable to move forward when it expands owing to loosening of the outer tube inside a body cavity or friction between the outer tube and the body cavity, between the outer tube and a catheter which introduces the outer tube or between the outer tube and a valve of a device called an introducer for introducing the delivery system into a patient's body.
Noting the above-described problem, the present applicant proposed the stent delivery system 1 disclosed in U.S. Patent Application Publication No. 2006/0259124. The stent delivery system 1 in this patent application publication includes a distal-side tube 2 having the guide wire lumen 21, a proximal-side tube 4 fixed to the proximal portion of the distal-side tube 2, a stent accommodation tubular member 5 which encloses the distal side of the distal-side tube 2 and is slidable in the proximal direction, a stent 3 accommodated inside the tubular member 5, and a pulling wire 6 for moving the tubular member 5 toward the proximal side. The distal-side tube 2 has a proximal-side opening 23, a stent-locking portion 22 for preventing the stent from moving toward the proximal side, and a operation part having the pulling wire winding mechanism and the wire winding amount prevention mechanism.
The stent delivery system 1 further includes an intermediate tube 7 which encloses the proximal side of the distal-side tube 2 and the proximal side of the stent accommodation tubular member 5 and is fixed to the proximal portion of the distal-side tube 2 and to the distal portion of the proximal-side tube 4 at the proximal portion thereof. The intermediate tube 7 encloses the proximal side of the distal-side tube 2 and the proximal side of the stent accommodation tubular member 5 without preventing the stent accommodation tubular member 5 from moving toward the proximal side. One end portion of the pulling wire 6 is fixed to the stent accommodation tubular member 5 inside the intermediate tube 7. The pulling wire 6 passes between the intermediate tube 7 and the distal-side tube 2, thus extending into the proximal-side tube 4.
Even though the self-expandable stent is used with the stent delivery system, the proximal-side opening is disposed not at the proximal end of an appliance, but at the proximal side of the distal-side tube. Therefore in a stent-implanting operation, an operation of exchanging the stent delivery system with other stent delivery systems can be relatively easily performed. By pulling the pulling wire toward the proximal side, the stent can be discharged. Therefore in a stent-discharging operation, the stent is moved in a very small amount. Further the stent delivery system has an advantage that in pulling a stent-binding member toward the proximal side, because the wire is not wound in an excessive amount, a catheter is prevented from being unnecessarily curved or damaged.
The stent delivery system disclosed in U.S. Patent Application Publication No. 2006/0259124 is sufficiently effective. With this stent delivery system, while inserting the stent into an organism, situations arise in which an insertion operation is performed by imparting a twist (torque) at the proximal side. The twist imparted at the proximal side may be transmitted to the stent accommodation tubular member through the distal portion of the intermediate tube. The twist imparted to the stent accommodation tubular member is also imparted to the stent accommodated therein with the inner surface thereof being pressed. The present inventors have found it is desirable not to impart the twist to the stent.